The present invention relates to a spinel type ceramic sintered body and a method of producing same, and more particularly a sintered body of spinel type ceramic particularly comprised by adding an aluminium silicate powder containing at least a clay into a chrom slag discharged as waste from sodium chromate production and reaction-sintering said mixture to form a ceramic sintered body, said sintered body being characterized by having excellent thermal conductivity, mechanical strength, magnetic properties and the like and capable of being used for functional tiles, for example.
In the commercial production of sodium chromate, a method has been commonly employed, wherein alkali agents such as soda ash and/or sodium hydroxide, if necessary, lime or an inert filler are mixed in a chromium ore, the resultant mixture then being subjected to an oxidative roasting at an elevated temperature and the roasted product thus obtained being subsequently leached with water to produce sodium chromate as an aqueous solution, at which time a great amount of chrom slag (simply referred to as chrom slag hereafter) is produced as a by-product.
Since hazardous hexavalent chromium is contained in said slag, dumping it without any treatment would pollute the soil and water causing enviromental pollution, hence methods for making it non-hazardous have been employed. Among these include a method which reduces the hexavalent chromium to a trivalent one by directly adding a reducing agent to the chrom slag or another method in which reduction of chrom slag at a high temperature is carried out by adding a silicate material and a reducing agent, but presently in either case the treated waste material is merely dumped or utilized as an earth filling material or an aggregate.
On the other hand, the present applicants have developed processes for applying the chrom slag in the ceramics field as an effective utilization of chrom slag and filed the following patent applications; Japanese Patent Application Laid Open Nos. 51-41009, 51-81806, and 59-92968.
However, since in terms of its properties, chrom slag has a great deal of variety in its physical characteristics not to mention in its chemical compositions, when trying to effectively utilize it industrially reproducability was remarkably lacking not only in the step of producing ceramic products but also in all the various physical and chemical characteristics of the produced ceramics.
Although normal chrom slag contains a calcium component, it was found that ceramic products manufactured using high calcium containing chrom slag have a problem in that such ceramics are inferior both in functions and durability. In view of the above facts, the applicants, intending to positively utilize the chrom slag effectively, eagerly carried out research aimed at improving the physical characteristics and methods of producing ceramic sintered bodies having chrom slag as the main raw material, whereupon the special features that are exhibited when a chrom slag having a specific chemical composition is used as a ceramic raw material were discovered and furthermore, it was also confirmed that the above fact is reproducable in the same way using other materials without being limited to the use of chrom slag as long as they are formulated to said specific chemical composition, hence arriving at the present invention.